Following amendment to the Kansas Constitution in 1986, the county remained a prohibition, or "dry", county until 2000, when voters approved the sale of alcoholic liquor by the individual drink without a food sales requirement.[5]

According to the U.S. Census Bureau, the county has a total area of 572 square miles (1,480 km2), of which 571 square miles (1,480 km2) is land and 1.2 square miles (3.1 km2) (0.2%) is water.[6] The Wolf River has its source in the county.[7]Brown State Fishing Lake, formerly known as "Brown County State Park" is in the county, 8 miles (13 km) east of Hiawatha.

There were 4,318 households out of which 31.40% had children under the age of 18 living with them, 55.80% were married couples living together, 9.20% had a female householder with no husband present, and 31.70% were non-families. 28.80% of all households were made up of individuals and 15.70% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 2.99.

In the county the population was spread out with 26.40% under the age of 18, 7.40% from 18 to 24, 24.00% from 25 to 44, 22.70% from 45 to 64, and 19.50% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 93.50 males. For every 100 females age 18 and over, there were 89.80 males.

The median income for a household in the county was $31,971, and the median income for a family was $39,525. Males had a median income of $29,163 versus $19,829 for females. The per capita income for the county was $15,163. About 10.60% of families and 12.90% of the population were below the poverty line, including 16.40% of those under age 18 and 11.80% of those age 65 or over.

Brown County is divided into ten townships. The cities of Hiawatha, Horton, and Sabetha are considered governmentally independent and are excluded from the census figures for the townships. In the following table, the population center is the largest city (or cities) included in that township's population total, if it is of a significant size.